This invention relates to a method of forming a pattern of conductor runs on a dielectric sheet.
A so-called hybrid integrated circuit comprises a sheet-form substrate of ceramic material having one or more electronic components, such as monolithic integrated circuit chips, adhered to an upper surface of the substrate. Each electronic component has at least two terminals. The substrate may be composed of multiple sheets of ceramic material, secured together by sintering. Conductor runs are formed on the upper surface of each sheet. The conductor runs on each sheet interconnect contact pads on that sheet. A contact pad on the upper sheet may be wire bonded to a terminal of an electronic component, connected to a contact pad of one of the lower sheets through a via in the upper sheet (and possibly one or more vias in the lower sheet(s)), or connected to a conductor run of a printed circuit board. A contact pad on a lower sheet may be connected to a contact pad of another sheet through one or more vias.
It is known to use a screen printing process for providing a desired pattern of conductor runs on a ceramic sheet. In this process, a conductive ink is printed onto the ceramic sheet when it is in the unfired, or green, state. The green ceramic sheet comprises alumina powder in a matrix of an organic binder material, such as the material sold by Monsanto Company under the trademark BUTVAR 60, and is flexible and quite tough. The ink comprises a suspension of tungsten powder in an organic vehicle, and the pattern is defined by conventional screen printing techniques. After printing, the green ceramic sheet is heated to a temperature of about 800.degree. C. in air in order to burn off the organic binder material and the organic vehicle, which decompose into carbon dioxide and water, and is then fired at a temperature of about 1700.degree.) C. in an atmosphere of hydrogen. During the firing operation, the tungsten is sintered to the ceramic material.
This conventional process is not suitable for manufacture of a small number of sheets, such as might be required for prototyping a hybrid circuit. In particular, it is not economical to manufacture a printing screen if only a few sheets are to be printed.
In a laser printer, a photoconductive drum is electrostatically charged and is then exposed using a scanning laser beam. The area that is exposed is the negative of a desired image. Accordingly, the charged area of the drum corresponds to the image. Charged toner powder is applied to the drum, and adheres to the drum only at those regions that have not been exposed by the laser beam. The toner particles are transferred to a sheet of paper and are fused thereto.
It is also known to print an image on paper having a surface coating of dielectric material by placing the paper on a grounded platen and electrostatically charging the surface coating in selected regions by use of a conductive stylus that is connected to a potential source. Toner powder is deposited on the coated paper and adheres to the paper only in the regions that have been charged. The toner powder is then fused.
Another method of forming an image on a sheet of paper involves placing the paper between a film of photoconductive material and a conductive platen. A bias is established between the film of photoconductive material and the platen, and therefore the paper is charged. The photoconductive material is exposed with the negative of the desired image, and accordingly the paper is partially discharged, resulting in a charge image that corresponds to the desired image. Toner powder is applied to the paper and adheres only to the charged regions. The toner powder that adheres to the paper is fused to the paper.
One kind of toner powder that is conventionally used in laser printers, comprises core particles of magnetic material, e.g. iron or iron oxide, coated with a fusible wax that contains a pigment. The magnetic nature of the core particles enables the powder to be brought into contact with the photoconductive drum of the laser printer using a magnetic brush. The toner particles, which have previously been electrostatically charged, are transferred electrostatically from the magnetic brush to the charged areas of the drum.
In other types of xerographic imaging devices that employ photoconductive drums, the toner powder is poured onto the drum from above, or is agitated by bubbling air through a bed of toner material and the drum is positioned so that its periphery passes through the bed of agitated toner material. Thus, it is not essential to use a magnetic brush in order to tone a charged surface.